A British-owned company has become the first foreign high-technology firm to locate in Montgomery County as a result of the county's European business recruiting drive last November, according to a county spokesman.

Optim Electronics Corp., an subsidiary of Optim Ltd. of England, has decided to locate in a 6,500-square-foot area on Industrial Drive in Gaithersburg, the spokesman said. That brings the number of completely-foreign-owned firms in the county to seven. The firms (three English, one French, one German and one Swedish) already employ 1,000 persons and have a total payroll of $15 million, a spokesman said.

Optim will have 10 employes in the beginning, but it plans to expand later, the spokesman said. The firm manufactures high-technology measurement and control equipment for computers.

In addition, Rixon Inc., a subsidiary of Sangamo Weston Co. of France, plans to expand by 25,000 square feet its 100,000-square-foot facility at the Montgomery Industrial Park, the county spokesman said. Rixon manufactures a device that allows computers to talk to each other using telephones.

The number of employes at Rixon is expected to grow from 525 to 800 by next year.

Knorr Brake Corp., the American subsidiary of Bremse GmbH of West Germany, also plans to expand by 6,000 square feet its facilities in Rockville, the spokesman said. Knorr manufactures brakes for trains, subways and other rapid-transit vehicles.

Last November Maryland economic and community development representatives as well as economic officials from different Maryland counties lobbied in several European countries to lure business here. Montgomery County officials said they developed 15 leads from the trip and plan two more announcements of foreign firms locating here in the next few weeks.